This disclosure relates to a liquid waste processing system for purifying liquid wastes containing dissolved or suspended impurities. More specifically, this disclosure relates to the removal of solid and dissolved radioactive wastes contained in liquid waste generated in nuclear power plants.
The viability of the continued operation of nuclear reactors in and around our present communities, and indeed the continued operation of all processes which produce liquid waste such as pulp and paper industries and food processing industries, depends heavily upon the ability of the utility or the industry to clean up the liquid wastes that are generated by the processes. If an appropriate degree of purification of the liquid wastes can be obtained, the resulting purified liquids can be released to the environment or recycled in the system leaving only the concentrated solid wastes to be disposed. Current concern for the purity of the environment has led to increasingly strict controls on the disposal of such waste streams. As one example, the U.S. AEC (now the NRC) has recently promulgated a "final environmental statement concerning numerical guides for design objectives and limiting conditions for operation to meet the criterion `as low as practicable` for radioactive material in light-water-cooled nuclear power reactor effluents." These guides establish minimum decontamination factors for liquid waste treatment processes. Briefly, the AEC requirement is that discharges of radioactive material from utility operated nuclear power plants be "as low as practicable."
The commonly practiced method employed to dispose of liquid wastes generated in nuclear power plant cycles consists of the evaporation of the waste feed streams. The resulting condensate is sufficiently clear of solids and radioactivity to be discharged freely and the resulting concentrate is contained (drummed or solidified) for controlled disposal.
The commonly practiced prior art techniques, however, have the disadvantages that they induce substantial capital and operating costs, require extensive maintenance, have lengthly start-up times and occupy large amounts of building space. Most prior art rad-waste systems employ forced-circulation evaporators which consume large amounts of steam cooling water and electricity. In addition, forced and natural circulation evaporators require highly complex instrumentation and controls in order to balance all the operating parameters involved in proper unit operation. Nuclear experience with these prior art units indicates that the controls are difficult to adjust and seldom work as designed.
Accordingly, a need is felt for a less expensive, less complex system which can process radioactive liquid waste with the production of a low-radioactive effluent which may be discharged to the environment without environmental degradation.